Double-arc Volumetric-modulated Arc Therapy Research Articles

Organ at risk dose verification in nasopharyngeal cancer VMAT planning with collimator comparison between single arc and double arc

Volumetric modulated arc therapy (VMAT) is an irradiation technique that enables the improvement of the flexibility of dose delivery from a full range of angles with continuous modulation of beam aperture and dose rate. We compared the homogeneity index (HI), conformity index (CI), dose volume histogram (DVH) and dose differentiation of single arc and double arc VMAT delivered for nasopharyngeal cancer (NPC). Planning for gantry rotation angles of 360° counter clockwise and clockwise (double arc) with collimator (0° and 10°) and 360° clockwise (single arc) were created for ten nasopharyngeal cancer cases applied in RANDO phantom with the Eclipse treatment planning system and delivered using Trilogy linear accelerator. The verification was performed by using gafchromic film EBT3 and placed on the RANDO phantom according to the location of the organs at risk. In this study, we evaluated right parotid, left parotid, right eye, left eye and trachea. The measurement of mean dose using gafchromic film and TPS shows that the resulting values were close to TPS results with the difference being −1.51%. From the result of dose measurement using gafchromic film based on the data from RANDO CT phantom use, it can be concluded that double arc VMAT technique with collimator can reduce the dose in the organ at risk.

Log file-based patient dose calculations of double-arc VMAT for head-and-neck radiotherapy

PurposeThe log file-based method cannot display dosimetric changes due to linac component miscalibration because of the insensitivity of log files to linac component miscalibration. The purpose of this study was to supply dosimetric changes in log file-based patient dose calculations for double-arc volumetric-modulated arc therapy (VMAT) in head-and-neck cases. Methods and materialsFifteen head-and-neck cases participated in this study. For each case, treatment planning system (TPS) doses were produced by double-arc and single-arc VMAT. Miscalibration-simulated log files were generated by inducing a leaf miscalibration of ±0.5 mm into the log files that were acquired during VMAT irradiation. Subsequently, patient doses were estimated using the miscalibration-simulated log files. ResultsFor double-arc VMAT, regarding planning target volume (PTV), the change from TPS dose to miscalibration-simulated log file dose in Dmean was 0.9 Gy and that for tumor control probability was 1.4%. As for organ-at-risks (OARs), the change in Dmean was <0.7 Gy and normal tissue complication probability was <1.8%. A comparison between double-arc and single-arc VMAT for PTV showed statistically significant differences in the changes evaluated by Dmean and radiobiological metrics (P < 0.01), even though the magnitude of these differences was small. Similarly, for OARs, the magnitude of these changes was found to be small. ConclusionsUsing the log file-based method for PTV and OARs, the log file-based method estimate of patient dose using the double-arc VMAT has accuracy comparable to that obtained using the single-arc VMAT.

Validation of the relative insensitivity of volumetric-modulated arc therapy (VMAT) plan quality to gantry space resolution.

Volumetric-modulated arc therapy (VMAT) is an efficient form of radiotherapy used to deliver intensity-modulated radiotherapy beams. The aim of this study was to investigate the relative insensitivity of VMAT plan quality to gantry angle spacing (GS). Most previous VMAT planning and dosimetric work for GS resolution has been conducted for single arc VMAT. In this work, a quantitative comparison of dose–volume indices (DIs) was made for partial-, single- and double-arc VMAT plans optimized at 2°, 3° and 4° GS, representing a large variation in deliverable multileaf collimator segments. VMAT plans of six prostate cancer and six head-and-neck cancer patients were simulated for an Elekta SynergyS® Linac (Elekta Ltd, Crawley, UK), using the SmartArc™ module of Pinnacle³ TPS, (version 9.2, Philips Healthcare). All optimization techniques generated clinically acceptable VMAT plans, except for the single-arc for the head-and-neck cancer patients. Plan quality was assessed by comparing the DIs for the planning target volume, organs at risk and normal tissue. A GS of 2°, with finest resolution and consequently highest intensity modulation, was considered to be the reference, and this was compared with GS 3° and 4°. The differences between the majority of reference DIs and compared DIs were <2%. The metrics, such as treatment plan optimization time and pretreatment (phantom) dosimetric calculation time, supported the use of a GS of 4°. The ArcCHECK™ phantom–measured dosimetric agreement verifications resulted in a >95.0% passing rate, using the criteria for γ (3%, 3 mm). In conclusion, a GS of 4° is an optimal choice for minimal usage of planning resources without compromise of plan quality.

Total body irradiation’s dosimetric features by volumetric modulated ARC therapy method

Purpose To compare three different types of volumetric modulated arc therapy(VMAT) planning tecniques using Elekta Versa HD lineer accelerator to deliver total body irradition(TBI) treatment. Methods Five TBI patient’s treatment planning performed using Monaco5.1® treatment planning system with three different VMAT tecniques for each patient.First one was single arc VMAT tecnique, second one was double arc VMAT tecnique and third one was 2 fields arc VMAT tecnique for one isocentre.The VMAT-TBI tecnique consisted of three isocentres and three overlapping arcs.The prescribed dose was 95% of target volume receiving dose of 12 Gy.Mean dose to lung and kidney were restricted less than 9.0 Gy. Results An average total delivery time was determined 835 ± 86 seconds and an average monitor unit (MU)s was determined 2202 ± 254 MUs for double arc VMAT technique. This study demonstrates that double arc VMAT technique has got less MUs than other technique but an average delivery time is %17 more than single arc VMAT technique. When we compared organ at risk (OAR)s, we had less dose and better dose coverage to target with double arc VMAT technique. Conclusion The tecnique for TBI using VMAT was found feasible.The results show that dose coverage of target and OAR’s doses also depend significantly VMAT techniques. Based on the results we have decided to plan TBI in our clinic with double arc VMAT technique.

SU-G-BRC-03: A Novel Multi-Criteria Optimization Method for Volumetric Modulated Arc Therapy (VMAT) Treatment Planning

Purpose: To present a novel multi-criteria optimization (MCO) solution approach that generates treatment plans for VMAT. Methods: We demonstrate our method with generating double-arc VMAT plans for 10 locally advanced head-and-neck cancer cases retrospectively. In our MCO formulation, we defined an objective function for each structure in the treatment volume. This resulted in 9 objective functions, including 3 distinct objectives for primary, high-risk and low-risk target volumes, 5 objectives for each of the organs-at-risk (OARs) (two parotid glands, spinal cord, brain stem and oral cavity), and one for the non-target non-OAR normal tissue. Conditional value-at-risk (CVaR) constraints were utilized to ensure at least certain fraction of the PTVs receiving the prescription doses. Besides formulating the problem as MCO, our approach directly generated weight and aperture for each control point considering MLC connectivity constraints, leaf speed, gantry speed, gantry speed change and dose rate utilizing column generation algorithm. Final dose distributions for all plans were compared after a Monte Carlo kernel-superposition dose calculation. Results: We compared our method with clinical VMAT plans and segment weight optimization (SWO) of the clinical plans. At least 95% target coverage was achieved by all plans. However, the average of the conformity indices for MCO was 1.28 comparing to clinical VMAT 1.83 (30% reduction, p<0.01) and SWO 1.63 (22% reduction, p<0.01). MCO method achieved reduction in right parotid mean dose of 17% (p<0.01) and 10% (p=0.03), oral cavity mean dose of 23% (p<0.01) and 6% (p=0.34) and spinal cord maximum dose of 20% (p<0.01) and 10% (p<0.01), brain stem maximum dose of 59% (p<0.01) and 57% (p<0.01), and normal tissue maximum dose of 4% (p<0.01) and 5% (p<0.01), comparing to clinical VMAT and SWO respectively. Conclusion: We demonstrated that the proposed MCO method was able to obtain VMAT plans with significant improvement in dosimetric plan quality.

Influence of multileaf collimator leaf width on volumetric modulated arc therapy plans evaluated on AAPM standard phantom

Objective To develop double-arc volumetric modulated arc therapy (VMAT) plans using standard phantom and standard target volume in AAPM119 report, and to investigate the dosimetric parameters of Agility and MLCi2 leafs according to the requirements for target dose in AAPM119 report. Methods The Cshape, Head and Neck, Prostate, and Multitarget structures for standard target volume delineation in AAPM119 report were used. The Elekta Agility multi-leaf collimator was used to develop plans, and then with other parameters remaining unchanged, Elekta MLCi2 was used for plan optimization and dose calculation. The target dose in AAPM119 report was used as the standard to analyze the differences in target volume and dose-volume parameters of organs at risk between the four structures for target volume delineation. Results According to the mean dose in AAPM119 report, in the Cshape, Head and Neck, and Multitarget target volumes, the radiotherapy plans developed with Agility had better dosimetric parameters compared with those developed with MLCi2. In the prostate target volume, the radiotherapy plans developed with MLCi2 had better dosimetric parameters compared with those developed with Agility. Conclusions With the structures for target volume delineation, plan designing personnel, designing parameters, and evaluation criteria remaining the same, Elekta Agility can achieve the dose target better than Elekta MLCi2 in the aspect of strict dose limit. Key words: Multi-leaf collimator; Leaf width; Volumetric modulated arc therapy; Dosimetry

Volumetric modulated arc therapy for carotid sparing in the management of early glottic cancer.

PurposeRadiotherapy of the neck is known to cause carotid artery stenosis. We compared the carotid artery dose received between volumetric modulated arc therapy (VMAT) and conventional fixed-field intensity-modulated radiotherapy (IMRT) plans in patients with early glottic cancer.Materials and MethodsTwenty-one early glottic cancer patients who previously underwent definitive radiotherapy were selected for this study. For each patient, double arc VMAT, 8-field IMRT, 3-dimensional conformal radiotherapy (3DCRT), and lateral parallel-opposed photon field radiotherapy (LPRT) plans were created. The 3DCRT plan was generated using lateral parallel-opposed photon fields plus an anterior photon field. VMAT and IMRT treatment plan optimization was performed under standardized conditions to obtain adequate target volume coverage and spare the carotid artery. Dose-volume specifications for the VMAT, IMRT, 3DCRT, and LPRT plans were calculated with radiotherapy planning system. Monitor units (MUs) and delivery time were measured to evaluate treatment efficiency.ResultsTarget volume coverage and homogeneity results were comparable between VMAT and IMRT; however, VMAT was superior to IMRT for carotid artery dose sparing. The mean dose to the carotid arteries in double arc VMAT was reduced by 6.8% compared to fixed-field IMRT (p < 0.001). The MUs for VMAT and IMRT were not significantly different (p = 0.089). VMAT allowed an approximately two-fold reduction in treatment delivery time in comparison to IMRT (3 to 5 minutes vs. 5 to 10 minutes).ConclusionVMAT resulted in a lower carotid artery dose compared to conventional fixed-field IMRT, and maintained good target coverage in patients with early glottic cancer.

An investigation of the dose distribution effect related with collimator angle in volumetric arc therapy of prostate cancer.

To investigate the dose-volume variations of planning target volume (PTV) and organ at risks (OARs) in eleven prostate cancer patients planned with single and double arc volumetric modulated arc therapy (VMAT) when varying collimator angle. Single and double arc VMAT treatment plans were created using Monaco5.0® with collimator angle set to 0°. All plans were normalized 7600 cGy dose to the 95% of clinical target volume (CTV) volume. The single arc VMAT plans were reoptimized with different collimator angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°), and for double arc VMAT plans (0–0°, 15°–345, 30–330°, 45–315°, 60–300°, 75–285°, 90–270°) using the same optimization parameters. For the comparison the parameters of heterogeneity index (HI), dose-volume histogram and minimum dose to the 95% of PTV volume (D95 PTV) calculated and analyzed. The best plans were verified using 2 dimensional ion chamber array IBA Matrixx® and three-dimensional IBA Compass® program. The comparison between calculation and measurement were made by the γ-index (3%/3 mm) analysis. A higher D95 (PTV) were found for single arc VMAT with 15° collimator angle. For double arc, VMAT with 60–300° and 75–285° collimator angles. However, lower rectum doses obtained for 75–285° collimator angles. There was no significant dose difference, based on other OARs which are bladder and femur head. When we compared single and double arc VMAT's D95 (PTV), we determined 2.44% high coverage and lower HI with double arc VMAT. All plans passed the γ-index (3%/3 mm) analysis with more than 97% of the points and we had an average γ-index for CTV 0.36, for PTV 0.32 with double arc VMAT. These results were significant by Wilcoxon signed rank test statistically. The results show that dose coverage of target and OAR's doses also depend significantly on the collimator angles due to the geometry of target and OARs. Based on the results we have decided to plan prostate cancer patients in our clinic with double arc VMAT and 75°–285° collimator angles.

Comparison of hybrid volumetric modulated arc therapy (VMAT) technique and double arc VMAT technique in the treatment of prostate cancer.

BackgroundVolumetric modulated arc therapy (VMAT) has quickly become accepted as standard of care for the treatment of prostate cancer based on studies showing it is able to provide faster delivery with adequate target coverage and reduced monitor units while maintaining organ at risk (OAR) sparing. This study aims to demonstrate the potential to increase dose conformality with increased planner control and OAR sparing using a hybrid treatment technique compared to VMAT.MethodsEleven patients having been previously treated for prostate cancer with VMAT techniques were replanned with a hybrid technique on Varian Treatment Planning System. Multiple static IMRT fields (2 to 3) were planned initially based on critical OAR to reduce dose but provide some planning treatment volume (PTV) coverage. This was used as a base dose plan to provide 30–35% coverage for a single arc VMAT plan.ResultsThe clinical VMAT plan was used as a control for the purposes of comparison. Average of all OAR sparing between the hybrid technique and VMAT showed the hybrid plan delivering less dose in almost all cases except for V80 of the bladder and maximum dose to right femoral head. PTV coverage was superior with the VMAT technique. Monitor unit differences varied, with the hybrid plan able to deliver fewer units 37% of the time, similar results 18% of the time, and higher units 45% of the time. On average, the hybrid plan delivered 10% more monitor units.ConclusionsThe hybrid plan can be delivered in a single gantry rotation combining aspects of VMAT with regions of dynamic intensity modulated radiation therapy (IMRT) within the treatment arc.

BM-04 * IMAGE GUIDED STEREOTACTIC RAPID ARC(R) TO SINGLE BRAIN METASTATIC ASSISTED BY INTRACRANIAL CALCIFICATION

BACKGROUND: Image-guided radiation therapy (IGRT) cone-beam CT (CBCT) is delivering important improvements in the stereotactic radiotherapy. Volumetric Modulated Arc Therapy (VMAT), known as Rapid Arc® from Varian Medical Systems has the ability to deliver radiation in less time and treat several targets simultaneously. METHODS: We review a single case report of 82 yrs. old, female, with a contrast magnetic resonance diagnosis of enhanced single left occipital lobe brain metastases from a colorectal cancer. ECOG 1. The mental and neurologic physical examination is age-appropriate. Maximum diameter size of the single lesion was 3.8 cm (volume: 33.3 cm3). Previous immobilization with a thermoplastic head mask and brain CT scan for planning were done. Whole brain radiotherapy with simultaneous integrated boost (WBRT&SIB) for dual Rapid Arc® was planned after delineated planning tumor volume (PTV) and organs at risks (OAR). The prescribed dose to metastatic lesion (PTV 1) was 37,5Gy and normal brain (PTV 2) in 25Gy, both PTV in 10 fractions (2 weeks). A daily CBCT was applied with the auxiliary use of natural intracranial calcifications for improve the frameless position of the targets. Shift table displacements after setup using online CBCT in anterior-posterior (AP), right-left (RL), superior-inferior (SI) directions was annotated in centimeters +/- standard deviation (cm +/- SD). RESULTS: Mean dose for PTV 1 and PTV 2 was 38.9 Gy and 26.8 Gy respectively. PTV 1 Conformity Index (CI) was 1.06. Mean +/- SD residual setup shift table displacements were registered in AP: -0.01 +/- 0.06 cm; RL: -0.04 +/- 0.14 cm; SI: -0.14 +/- 0.14 cm. CONCLUSION: IN this only patient experience, frameless double arc VMAT WBRT&SIB was optimal delivered with the use of online CBCT and intracranial calcifications reposition.

VMAT planning study in rectal cancer patients.

BackgroundTo compare the dosimetric differences among fixed field intensity-modulated radiation therapy (IMRT), single-arc volumetric-modulated arc therapy (SA-VMAT) and double-arc volumetric-modulated arc therapy (DA-VMAT) plans in rectal cancer.MethodFifteen patients with rectal cancer previously treated with IMRT in our institution were selected for this study. For each patient, three plans were generated with the planning CT scan: one using a fixed beam IMRT, and two plans using the VMAT technique: SA-VMAT and DA-VMAT. Dose prescription to the PTV was 50 Gy in 2 Gy per fraction. Dose volume histograms (DVH) for the target volume and the organs at risk (small bowel, bladder, femoral heads and healthy tissue) were compared for these different techniques. Monitor units (MU) and delivery treatment time were also reported.ResultsDA-VMAT achieved the highest minimum planning target volume (PTV) dose and the lowest maximal dose, resulting in the most homogeneous PTV dose distribution. DA-VMAT also yielded the best CI, although the difference was not statistically significant. Between SA-VMAT and IMRT, the target dose coverage was largely comparable; however, SA-VMAT was able to achieve a better V95 and V107. VMAT showed to be inferior to IMRT in terms of organ at risk sparing, especially for the small bowel. Compared with IMRT, DA-VMAT increased the V15 of small bowel nearly 55 cc. The MU and treatment delivery time were significantly reduced by the use of VMAT techniques.ConclusionVMAT is a new radiation technique that combines the ability to achieve highly conformal dose distributions with highly efficient treatment delivery. Considering the inferior role of normal tissue sparing, especially for small bowel, VMAT need further investigation in rectal cancer treatment.

Sci-Sat AM: Stereo - 08: Stereotactic Ablative Radiotherapy (SABR) for low, intermediate and high risk prostate cancer using Volumetric Modulated Arc Therapy (VMAT) with a 10x Flattening Filter Free (FFF) beam

Purpose: To determine the feasibility of using Volumetric Modulated Arc Therapy (VMAT) with a 10x Flattening Filter Free (FFF) beam for Stereotactic Ablative Radiotherapy (SABR) for low, intermediate and high risk prostate cancer. Methods and Materials: Ten anonymized patient CT data sets were used in this planning study. For each patient CT data set, three sets of contours were generated: 1) low risk, 2) intermediate risk, and 3) high risk scenarios. For each scenario, a single-arc and a double-arc VMAT treatment plans were created. Plans were generated with the Varian Eclipse™ treatment planning system for a Varian TrueBeam™ linac equipped with Millenium 120 MLC. Plans were created using a 10x-FFF beam with a maximum dose rate of 2400 MU/min. Dose prescription was 36.25Gy/5 fractions with the planning objective of covering 99% of the Planning Target Volume with the 95% of the prescription dose. Normal tissue constraints were based on provincial prostate SABR planning guidelines, derived from national and international prostate SABR protocols. Plans were evaluated and compared in terms of: 1) dosimetric plan quality, and 2) treatment delivery efficiency. Results: Both single-arc and double-arc VMAT plans were able to meet the planning goals for low, intermediate and high risk scenarios. No significant dosimetric differences were observed between the plans. However, the treatment time was significantly lower for a single-arc VMAT plans. Conclusions: Prostate SABR treatments are feasible with 10x-FFF VMAT technique. A single-arc VMAT offers equivalent dosimetric plan quality and a superior treatment delivery efficiency, compared to a double-arc VMAT.

Volumetric Modulated Arc Radiotherapy for Early Stage Non-Small-Cell Lung Carcinoma: Is It Better Than the Conventional Static Beam Intensity Modulated Radiotherapy?

This study compared the performance of volumetric modulated arc therapy (VMAT) techniques: single arc volumetric modulated arc therapy (SA-VMAT) and double arc volumetric modulated arc therapy (DA-VMAT) with the static beam conventional intensity modulated radiotherapy (C-IMRT) for non-small-cell lung carcinoma (NSCLC). Twelve stage I and II NSCLC patients were recruited and their planning CT with contoured planning target volume (PTV) and organs at risk (OARs) was used for planning. Using the same dose constraints and planning objectives, the C-IMRT, SA-VMAT, and DA-VMAT plans were optimized. C-IMRT consisted of 7 static beams, while SA-VMAT and DA-VMAT plans consisted of one and two full gantry rotations, respectively. No significant difference was found among the three techniques in target homogeneity and conformity. Mean lung dose in C-IMRT plan was significantly lower than that in DA-VMAT planP=0.04. The ability of OAR sparing was similar among the three techniques, with no significant difference inV20,V10, orV5of normal lungs, spinal cord, and heart. Less MUs were required in SA-VMAT and DA-VMAT. Besides, SA-VMAT required the shortest beam on time among the three techniques. In treatment of early stage NSCLC, no significant dosimetric superiority was shown by the VMAT techniques over C-IMRT and DA-VMAT over SA-VMAT.

Assessing the feasibility of volumetric-modulated arc therapy using simultaneous integrated boost (SIB-VMAT): An analysis for complex head-neck, high-risk prostate and rectal cancer cases

Intensity-modulated radiotherapy (IMRT) allowed the simultaneous delivery of different doses to different target volumes within a single fraction, an approach called simultaneous integrated boost (SIB). As consequence, the fraction dose to the boost volume can be increased while keeping low doses to the elective volumes, and the number of fractions and overall treatment time will be reduced, translating into better radiobiological effectiveness. In recent years, volumetric-modulated arc therapy (VMAT) has been shown to provide similar plan quality with respect to fixed-field IMRT but with large reduction in treatment time and monitor units (MUs) number. However, the feasibility of VMAT when used with SIB strategy has few investigations to date. We explored the potential of VMAT in a SIB strategy for complex cancer sites. A total of 15 patients were selected, including 5 head-and-neck, 5 high-risk prostate, and 5 rectal cancer cases. Both a double-arc VMAT and a 7-field IMRT plan were generated for each case using Oncentra MasterPlan treatment planning system for an Elekta Precise linac. Dosimetric indexes for targets and organs at risk (OARs) were compared based on dose-volume histograms. Conformity index, homogeneity index, and dose-contrast index were used for target analyses. The equivalent uniform doses and the normal tissue complication probabilities were calculated for main OARs. MUs number and treatment time were analyzed to score treatment efficiency. Pretreatment dosimetry was performed using 2-dimensional (2D)-array dosimeter. SIB-VMAT plans showed a high level of fluence modulation needed for SIB treatments, high conformal dose distribution, similar target coverage, and a tendency to improve OARs sparing compared with the benchmark SIB-IMRT plans. The median treatment times reduced from 13 to 20 minutes to approximately 5 minutes for all cases with SIB-VMAT, with a MUs reduction up to 22.5%. The 2D-array ion-chambers' measurements reported an agreement of more than 95% for a criterion of 3% to 3mm. SIB-VMAT was able to combine the advantages of conventional SIB-IMRT with its highly conformal dose distribution and OARs sparing and the advantages of 3D-conformal radiotherapy with its fast delivery.

Beam controlled arc therapy–a delivery concept for stationary targets

Volumetric modulated arc therapy (VMAT) presupposes that it is beneficial to deliver radiation from all beam angles as the gantry rotates, requiring the multi-leaf collimator to maintain continuity in shape from one angle to another. In turn, radiation from undesirable beam angles could compromise the dose distribution. In this work, we challenge the notion that the radiation beam must be held on as the gantry rotates around the patient. We propose a new approach for delivering intensity-modulated arc therapy, beam-controlled arc therapy (BCAT), during which the radiation beam is controlled on or off and the dose rate is modulated while the gantry rotates around the patient. We employ linear-programming-based dose optimization to each aperture weight, resulting in some zero weight apertures. During delivery, the radiation beam is held off at control points with zero weights as the MLC shape transits to the next non-zero weight shape. This was tested on ten head and neck cases. Plan quality and delivery efficiency were compared with VMAT. Improvements of up to 17% (p-value 0.001) and 57% (p-value 0.018) in organ-at-risk sparing and target dose uniformity, respectively, were achieved. Compared to the fixed number of apertures used in single-arc and double-arc VMAT, the BCAT used 109 and 175 apertures on average, respectively. The difference in total MUs for VMAT and BCAT plans was less than 4%. Plan quality improvement was confirmed after delivery with γ analysis resulting in over 99% agreement, or 4 in 1099 points that failed.

Using overlap volume histogram and IMRT plan data to guide and automate VMAT planning: A head-and-neck case study

To investigate whether an overlap volume histogram (OVH)-driven planning application using an intensity-modulated radiation therapy (IMRT) database can guide and automate volumetric-modulated arc therapy (VMAT) planning for head-and-neck cancer. Based on comparable head-and-neck dosimetric results between planner-generated VMAT and IMRT plans, an inhouse developed, OVH-driven automated planning application containing a database of prior clinical head-and-neck IMRT plans is built into Pinnacle(3) SmartArc for VMAT planning. Double-arc VMAT plans of four oropharynx, four nasopharynx, and four larynx patients are generated and compared with corresponding clinical IMRT plans. Each VMAT plan is automatically generated in two optimization rounds, while the average number of optimization rounds in generating a clinical IMRT plan is 43. In VMAT plans, statistical superiority (p < 0.01) in sparing of the cord+4 mm, brainstem, brachial plexus, larynx, and inner ear is observed with a slight degradation in low-dose-level planning target volume (PTV) coverage. On average, D(0.1 cc) to the cord+4 mm, brainstem and brachial plexus is reduced by 3.7, 4.9, and 1.6 Gy, respectively; V(50 Gy) to the larynx is reduced by 5.3%; mean dose to the inner ear is reduced by 4.4 Gy; V(95) of low-dose-level PTV coverage is reduced by 0.3% with p = 0.25. IMRT-data-driven VMAT planning offers a potential method for generating VMAT plans that are comparable to IMRT plans in terms of dosimetric quality.

Comparison of Step-and-Shoot IMRT and Different Volumetric Modulated Arc Therapy (VMAT) Techniques for the Treatment of Prostate Cancer

Dose escalation in the treatment of prostate cancer improves local control; however higher doses also carry the risk of late morbidity. Modern radiation therapy techniques such as IMRT and VMAT provided better tumor control and sparing of organs-at-risk (OAR) have been achieved. The purpose of this study is to compare step-and-shoot IMRT, single arc and double arc VMAT techniques regarding plan quality and efficiency of treatment delivery.

Poster - Thur Eve - 61: A dosimetric comparison between single-arc and double-arc prostate VMAT plans.

This study compared the dosimetry between prostate plans using the single-arc and double-arc technique in volumetric modulated arc therapy (VMAT). Single-arc and double-arc prostate VMAT plans were created in five patients with prostate volumes ranging from 39.0-68.1 cm3 . 6 MV photon beams generated by a Varian 21EX linac with 120-leaf multileaf collimator, and prescription dose of 78 Gy with 39 fractions were used. Dose-volume histograms of the target and critical organs, dose criteria such as the planning target volume (PTV) D99%, rectum D30% and rectum D50%, and dose profiles along the anterior-posterior and lateral directions crossing the isocenter were determined using the Eclipse treatment planning system with RapidArc optimization. It is found that the double-arc technique provided a better PTV coverage and rectal sparing compared to the single-arc for all patients. For dose profiles crossing the isocenter, it is seen that the dose in the anterior-posterior direction was shifted to the lateral, when the single-arc technique was replaced by the double-arc. This dosimetric change made the dose in the rectal position shift laterally to the femoral head, resulting in a lower rectal dose. The calculated monitor units (MUs) were 471-600 for the single-arc plans and 587-730 for the double-arc. Although the double-arc plans on average required more MUs of about 20%, and almost twice the treatment time compared to the single-arc, it is worthwhile to be considered particularly in some cases, where the dose criteria are difficult to achieve using the single-arc technique.

Dosimetric comparison of volumetric modulated arc therapy and intensity-modulated radiation therapy for pancreatic malignancies

Volumetric-modulated arc therapy (VMAT) has been previously evaluated for several tumor sites and has been shown to provide significant dosimetric and delivery benefits when compared with intensity-modulated radiation therapy (IMRT). To date, there have been no published full reports on the benefits of VMAT use in pancreatic patients compared with IMRT. Ten patients with pancreatic malignancies treated with either IMRT or VMAT were retrospectively identified. Both a double-arc VMAT and a 7-field IMRT plan were generated for each of the 10 patients using the same defined tumor volumes, organs at risk (OAR) volumes, dose, fractionation, and optimization constraints. The planning tumor volume (PTV) maximum dose (55.8 Gy vs. 54.4 Gy), PTV mean dose (53.9 Gy vs. 52.1 Gy), and conformality index (1.11 vs. 0.99) were statistically similar between the IMRT and VMAT plans, respectively. The VMAT plans had a statistically significant reduction in monitor units compared with the IMRT plans (1109 vs. 498, p < 0.001). In addition, the doses to the liver, small bowel, and spinal cord were comparable between the IMRT and VMAT plans. However, the VMAT plans demonstrated a statistically significant reduction in the mean left kidney V25 (9.4 Gy vs. 2.3 Gy, p = 0.018), mean right kidney V15 (53.4 Gy vs. 45.9 Gy, p = 0.035), V20 (32.2 Gy vs. 25.5 Gy, p = 0.016), and V25 (21.7 Gy vs. 14.9 Gy, p = 0.001). VMAT was investigated in patients with pancreatic malignancies and compared with the current standard of IMRT. VMAT was found to have similar or improved dosimetric parameters for all endpoints considered. Specifically, VMAT provided reduced monitor units and improved bilateral kidney normal tissue dose. The clinical relevance of these benefits in the context of pancreatic cancer patients, however, is currently unclear and requires further investigation.

Dose comparisons for conformal, IMRT and VMAT prostate plans

Volumetric-modulated arc therapy (VMAT) is a relatively new treatment technique in radiation therapy. A comparison study of conformal, intensity-modulated radiation therapy (IMRT) and single- and double-arc VMAT plans was undertaken to evaluate the dosimetric impact of this new technology in prostate cases. The research questions were as follows: how does VMAT dosimetry compare with IMRT and conformal plans?; does VMAT increase the volume of bowel receiving lower doses?; are one or two VMAT arcs required for standard prostate cases? Eight prostate cancer and post-prostatectomy patients were randomly selected for this study. Conformal, IMRT and single and double Arc VMAT plans were generated and dosimetric evaluations were performed. Each plan was prescribed a total of 75.6 Gy over a course of 42 fractions to the planning target volume (PTV). The Healthy Tissue Conformity Index and the conformation number results revealed the IMRT and two VMAT techniques to have superior dosimetry to the PTV compared with the conformal plans. The maximum dose delivered to the PTV was significantly higher with the single-arc VMAT technique compared with the conformal or double-arc VMAT plans. There were no significant differences between the planning techniques for the bladder and small bowel dosimetry. However, IMRT and VMAT plans delivered less radiation to the rectum and femoral heads, and a single-arc VMAT plan was optimal for the right femoral head and the two VMAT techniques were optimal to the IMRT plans for the left femoral head. Single- and double-arc VMAT consistently resulted in favourable or slightly superior dosimetry when compared with static gantry IMRT for prostate cases. Both the VMAT techniques and static gantry IMRT resulted in superior critical tissue sparing when compared with conformal plans.